The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment of any royalties thereon.
The present invention relates to a microwave divider and combiner apparatus and in particular for the monitoring of the reflected power caused by external divider impedance mismatches or external combiner phase errors.
Power dividers and combiners are used in many ways in microwave circuits. Two important examples are for combining power for transmission and for dividing power in preparation for creating separate phases for phased array antenna pointing. In either case it is highly desirable to have high insolation between output ports and to be able to dissipate all reflected power without disturbing the divider/combiner circuit through thermal heating.
In these dividers/combiners there are often separate microwave circuits comprising microwave directional couplers and microwave power measuring transducers used for the purpose of monitoring the combiner/divider and the follow-on microwave circuitry and/or antennas. These monitoring circuits may be used at the single input (for a divider) or at the single output (for a combiner) or can be duplicated N times for N outputs (for a divider) or N inputs (for a combiner). Such a monitoring method forces the use of extra parts (increasing weight, volume, and cost), increases insertion loss, and increases complexity of the original divider/combiner circuit.
As an example, transmitting phased-array antenna systems usually require that the transmitted power be divided N times and subsequently fed to different portions of the antenna array. Typical divider/combiners used are either reactive, Wilkinson, or Gysel type. The reactive divider has very poor isolation characteristics and furthermore cannot dissipate reflected power.
Wilkinson, U.S. Pat. No. 3,091,743, issued May 1963, and incorporated herein by reference, discloses a power divider. The Wilkinson type divider/combiner has high isolation but is not capable of high power use due to the layout topology of the reflect loads. As used in the present application, the terms xe2x80x9creflect loadxe2x80x9d, xe2x80x9creject loadxe2x80x9d are used interchangeably and will be referred to herein as xe2x80x9cisolation loadxe2x80x9d.
In the Gysel divider/combiner (See, e.g., Gysel, xe2x80x9cA New N-Way Power Divider/Combiner Suitable for High Power Applicationsxe2x80x9d, Proc of 1975, IEEE MTT Seminar, P. 116-118, incorporated herein by reference) does have high isolation characteristics with the added benefit of the ability to remote the reflect or isolation loads giving it high power capability.
After the transmitted power has been divided, the individual channels are then phased so that the antenna has the capability to xe2x80x9cpointxe2x80x9d RF/microwave power in more than one direction. Doppler beam swinging radar wind profilers (RWP) most often use this technique. A typical RWP system may use five to six separate phases and 24 to 150 separately fed antennas, with a correspondingly disperse RF cable corporate feed system. The individual phases may be created after the initial RF division by switching in delay lines of various predetermined lengths.
Due to the number of components involved from the divider all the way to the antennas (the divider, switches, cables, other dividers, and the antennas), component failure is not an uncommon occurrence. Detection of these failures can most directly be made through the measurement of reflected power during radar transmission periods. In actual application however, the use of many directional-couplers and RF power sensing devices is rarely used due to the previously mentioned issues.
Instead, maintaining the RWP at a high performance level is usually achieved through periodic antenna probing. To find any inoperative components, the radar operations are ceased and a RF vector network analyzer is used in conjunction with an external probe to measure insertion loss and phase through all possible paths (every phase and every antenna). This procedure may be performed whenever an operator suspects improper operation or typically every 6-12 months.
The present invention combines the divider/combiner functionality and the monitoring in one package. Although it is previously known that the Gysel type divider/combiner allows for monitoring of reflected power, no previously known device has directly used the heat dissipated by a isolation load for this purpose. Previously known devices rather rely on the aforementioned directional-coupler RF power sensing circuits.
The resultant invention is much simpler, weighs less, has no additional insertion loss, and is cheaper to implement than these previously mentioned methods. And because it is implemented directly on the isolation loads of the Gysel type divider/combiner, it allows increased ability to pinpoint which divider/combiner port has the impedance mismatch. Additionally, the reliability of the radar is not decreased by the invention nor the sensitivity degraded since this monitoring technique is completely noninvasive.
This invention is intended for use in the division of power for phased array radar systems or the combination of power from separate microwave devices. The device enables the continuous noninvasive monitoring of the operation of the divider/combiner or components connected to the ports of the divider/combiner.
The device is composed of a Gysel-type RF divider/combiner with the unique and novel addition of temperature measurement transducers located directly on the isolation loads. Since the Gysel divider/combiner is an inherently high isolation device, it avails itself to monitoring of single channel outputs (or inputs when used as a combiner) in terms of their individual reflected power.
A data acquisition system is used to measure the temperature of the isolation loads and the ambient temperature close to, but not effected by, the heat from the isolation loads. The difference in temperature between a isolation load and ambient will be indicative of external or internal component failure.
The isolation loads are printed circuit board type mounted planar high power resistors. By using a thermal epoxy, the temperature transducers can be placed directly on the high-power isolation loads. This also increases the response time and increases the sensitivity for reflected power measurement. The loads are coupled to external heat sinks to dissipate the heat. By combining both divider/combiner technology and direct single channel reflected power technology the device allows for load measurement without interfering with the RF signal.
The present invention may be used for many RF/microwave power combiner or divider applications where the operator is interested in knowing the operating quality of the divider/combiner, or the follow-on devices (for a divider) or input devices (for a combiner). To illustrate, as a combiner the invention could be used to indicate the condition and efficiency of input microwave amplifiers being combined as a single high power transmitter.
Also, for example, in a radar system whereby power is divided previous to being sent into a phased array antenna, the monitoring of the isolation loads gives a clear indication of the quality of operation of the divider and the follow-on cables, other dividers, and the antenna elements themselves.